Two-dimensional optical beam scanner

ABSTRACT

Described is an optical beam scanner capable of transmitting large beam diameters over wide fields of view in two dimensions (i.e., full-frame scanning) at high scan rates. A wide field of view in one dimension of the scan is achieved by focusing an incident beam on a rotating optical assembly in such a manner that the beam is collimated and deflected through an angle that is the sum of the angle subtended by an individual optical element of the assembly and the angle that develops due to the varying off-axis position of the beam with respect to the optical element.

JDU-O I lnventor Vlctnr .1. Non:

Towson, Md.

App]. No. 780,658

Filed Dec. 3, 1968 Patented Aug. 31, 1971 Assignee Westinghouse ElectricCorporation Pittsburgh, Pa.

TWO-DIMENSIONAL OPTICAL BEAM SCANNER jI/l Primary Examiner DavidSchonberg Assislan! Examiner-John W. Leonard Attorneys-F. H. Henson, E.P. Klipfel and J. L. Wiegrefi'e ABSTRACT: Described is an optical beamscanner capable of transmitting large beam diameters over wide fields ofview in two dimensions (i.e., full-frame scanning) at high scan rates. Awide field of view in one dimension of the scan is achieved by focusingan incident beam on a rotating optical assembly in such a manner thatthe beam is collimated and deflected through an angle that is the sum ofthe angle subtended by an individual optical element of the assembly andthe angle that develops due to the varying off-axis position ofthe beamwith respect to the optical element.

PATENIEI] Ausal m: 3 6 O2 57 2 SHEET 1 or 2 INVENTOR.

v ATTORNEY 3's VICTOR J. NORRIS, JR.

TWO-DIMENSIONAL OPTICAL BEAM SCANNER CROSS-REFERENCES TO RELATEDAPPLICATIONS Copending application Ser. No. 780,636, filed Dec. 3, 1968and assigned to the assignee of the present application.

BACKGROUND OF THE INVENTION In copending application Ser. No. 780,626,filed Dec. 3, 1968 and assigned to the assignee of the presentapplication an optical beam scanning system is shown which includes arotating disc having spaced around its periphery a number of lenses orspherical mirrors in side-by-side relationship. A pyramid that has thesame number of facets as there are optical elements is located in thecenter of the disc and rotates therewith. Each facet is located at thefocal point of its associated lens or mirror; while the beam to bescanned is focused on these reflective facets. The facets redirect thebeam to their companion lenses or mirrors; and as each optical elementrotates through the angle it subtends, it collimates the beam anddeflects it over this same angle. Further, since the principal axis ofthe lens is initially on one side of the beam, then coincident with it,and finally on the far side of the beam, an additional refractive angleis developed as a result of the off-axis position of the beam; and thedirection of this angle is such that it magnifies the rotational or scanangle generated.

The systems shown in the aforesaid copending application, while capableof providing angular displacements of large beam diameters over widefields of view, are generally limited to single line scanning. That is,they are not capable of scanning in two dimensions.

SUMMARY OF THE INVENTION As an overall object, the present inventionprovides a new and improved optical scanning system employing a rotatingmember having a plurality of optical elements spaced around itsperiphery, together with a truncated pyramid at the center of therotating member having facets which direct a beam of light throughsuccessive ones of the optical elements as the member rotates, andincorporating means for scanning in two dimensions.

Another object of the invention is to provide a two-dimensionalmechanical optical beam scanning system in which the field of view canbe varied to suit requirements.

In accordance with the invention, an optical scanning system is providedincluding a rotating disc having a number of lenses or spherical mirrorsspaced around its periphery. Carried at the center of the rotating discis a pyramid that has the same number of facets as there are opticalelements. Each facet is located at the focal point of its associatedlens or mirror; while the beam to be scanned is focused on one of thesereflective facets which redirects the beam to its companion lens. Aseach lens rotates through the angle it subtends, and because theprincipal axis of the lens shifts from one side of the beam to theother, the total angle scanned by the system in one dimension comprisesthe angle subtended by the optical element plus an additional refractiveangle which is developed as a result of the off-axis position of thebeam.

Scanning in the other dimension can be achieved by incorporation of arotating element within the lens system f the optical beam scanner. Therotating element, normally a polygon, preferably intercepts the beamprior to its being deflected by the aforesaid pyramid at a point wherethe beam is smaller than its ultimate transmitted size. Alternatively,two-dimensional scanning can be achieved by means of digital or opticaldeflecting devices, in which case the mechanical restrictions imposed bya rotating polygon are eliminated.

The above and other objects. and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIG. 1 illustrates the manner, in accordance with the invention, inwhich two angles are generated in concert to form a field of view in onedimension that is the sum of the two;

FIG. 2 depicts a typical configuration of the two-dimensional scanner ofthe invention wherein a rotating polygon is utilized to scan in onedimension and lenses are employed as the optical elements;

FIG. 3 is a top view of the scanner of FIG. 2;

FIG. 4 is an embodiment of the invention employing a rotating polygonand capable of producing an underscanned field of view;

FIG. 5 illustrates still another embodiment of the invention forexpanding the vertical field of scan by means of digital deflectors;

FIG. 6 illustrates still another embodiment of the invention employingan analog deflector for producing a vertical scan;

FIG. 7 illustrates the optical relationships involved in producing anoptical beam scanner with a continuously variable field of view; and

FIG. 8 is an embodiment of a typical two-dimensional scanner withvariable field of view capability.

With reference now to the drawings, and particularly to FIG. I, thepoint 10 represents the location of a stationary point light sourcelocated in the focal plane of a lens 12 which moves in the direction ofarrow 14 from the full-line position shown to the lower dotted lineposition. 8 indicates the angle through which the beam from source 10 isdeflected as the lens 12 rotates through the angle it subtends inrotating about axis 16. p indicates the angle through which the beam isrefracted by virtue of its initial and final off-axis positions. 7,therefore, is the total angle scanned by the beam; and it will bereadily appreciated that this angle is substantially larger than theangle traversed by the lens 12 about the axis I6. Thus, it can be seenthat the angle through which the beam is deflected is the sum of theangle subtended by the lens I2 and the angle that develops due to thevarying off-axis position of the beam with respect to the lens. As willbe seen, the lens 12 can be replaced, for example, by means of aspherical mirror.

With reference now to FIGS. 2 and 3, a typical configuration of thescanner for two-dimensional scanning is shown wherein lenses areemployed as the optical elements. The system includes a table or disc 18secured to a central shaft 20 and rotatable therewith. Circumferentiallyspaced around the periphery of the disc I8, on the top thereof, is aplurality of lenses 22, each having an axis extending through thecentral axis of the shaft 20, as perhaps best shown in FIG. 3. Alsomounted on the disc 18 and concentric with the shaft 20 is a truncatedpyramid 24 having a plurality of reflecting surfaces or facetscorresponding to the number of lenses 22, the arrangement being suchthat a beam of light directed against the facets will be reflectedthrough the lenses 22.

Above the pyramid 24 is a rotating polygon 26 having a plurality ofreflecting facets. To the left of the rotating polygon 26 is a laser rod28 surrounded by a flash tube 30. As will be appreciated, the laser rodis formed from paramagnetic material; and upon excitation by the flashtube 30 is capable of producing a beam 32 of monochromatic light. Thisbeam of monochromatic light is focused by lenses 34, 36 and 38onto ajagetsftherotating polyggn 2,6 where it is reflected down onto thefacets of the rotating pyramid 24, the focal point of the lens 38 beingat the surface of the facets on pyramid 24.

The light beam, after being reflected from the facets of 24, passesthrough an associated one of the lenses 22 and onto a distant object 40.The reflected light passes through one of a plurality of lenses 42circumferentially spaced around the periphery of a lower disc 44 alsoprovided with a truncated pyramid 46 having a plurality of reflectingfacets or surfaces corresponding to the number of facets on pyramid 24and aligned therewith. The light, after being focused into a point 48 ona facet of the truncated pyramid 46, is directed through a stationarylens 50 onto a photosensitive device, such as a photomultiplier 42.

Preferably, a single motor 44 drives both the rotating shaft 20 as wellas the polygon 26. The motor 44, for example, is connected to shaft 20through gear reducer 46; while it is connected to the rotating polygon26 through gear reducer 48 such that the speed of rotation of thepolygon is much greater than that of the shaft 20. In this manner, thepolygon 26 is made to rotate and causes the beam to scan up and down inthe vertical direction many times as the beam is caused to traverse ahorizontal field of scan, thereby producing twodimensional or full-framescanning. As will be appreciated, however, only the increased angle ofscan due to the refractive angles shown in FIG. I is achieved in thehorizontal direction, the vertical scan being determined by the size ofthe facets on the rotating polygon 26.

A system for underscanning in the horizontal direction is shown in FIG.4 and again includes a rotating disc 54 having a plurality of lenses 56circumferentially spaced around its periphery. A first truncated pyramid58 having a plurality of reflecting facets is carried on the rotatingdisc 54; while a second truncated pyramid 62 is carried above the firstand has a plurality of reflecting facets aligned with those of thetruncated pyramid 58. The two pyramids 58 and 62 are arranged such thata light beam incident on the upper pyramid 62 will be deflected to thelower pyramid at a point 60 where the principal axis of the outputoptical element and a facet of the pyramid intersect. As the entireassembly rotates, the beam will always be located on the principal axisof the output element and no refractive angles will be generated asshown in FIG. 1. Thus, an incident beam 64 passing through a stationaryinput lens 66 is directed onto a facet of the upper pyramid 62, thenceonto the facets of a rotating polygon 68, and then down onto a facet ofthe lower pyramid 58. From the facet of the lower pyramid 58, the lightis directed through the lens 56.

The rotating polygon 68 rotates about a stationary axis such that thebeam will always be located on the principal axis of the output lens 56and will not sweep across the facet as shown in FIG. 1. Consequently,the conditions required for generation of a refractive angle as shown inFIG. 1 are not satisfied, and only the rotational angle is generated andscanned in the horizontal direction in the same time period as isnormally used to generate both the refractive and rotational angles. Thearrangement of FIG. 4, however, does not alter the vertical scan fieldof view.

As will be appreciated, the two rotating reflecting elements shown inthe embodiment of the invention of FIG. 2, for example, require a rathercomplicated mechanical assembly. lf large beam diameters are employed inan effort to ultimately bring the beam to a sharp focus or to project ahighly collimated beam, these rotating elements become quite large. Thelarge sizes limit the scanner to somewhat slow scan rates, are heavy,require large volumes, and usually adversely influence structural anddynamic considerations.

A system for generating two-dimensional scans which does not require asmany mechanical components as that of FIG. 2 is shown in FIG. 5. Itagain includes a circular disc 70 mounted for rotation on a rotatingshaft 72 and provided with a truncated pyramid 74 having a plurality ofreflecting facets. A stationary light beam 76 is directed through astationary lens 78 onto the facets of the rotating pyramid 74, andthence through the rotating lenses 80 spaced around the periphery of thedisc 70.

In this case, each of the lenses 80 is disposed at an angle )3 betweenthe plane of the lens and horizontal (i.e., normal to the plane ofrotation). The angles B vary for each lens 80. Note. for example, thatthe angle 3 for the lens 80 to the right of shaft 72 projects radiallyoutwardly from horizontal; while the angle for the lens 80 to the leftof shaft 72 extends radially inwardly. Thus, as the disc 70 rotates, thebeam is deflected one increment in the vertical direction each time alens 80 rotates past the light beam.

This vertically deflected beam is then applied to a first electroopticaldigital deflector 82 where the beam can be deflected as beam 84 or beam86. Assuming that the incident beam is deflected as beam 84, it isapplied to a second digital deflector 88 where it can be deflected aseither beam 90 or beam 92. Similarly, assuming that the incident beam isdeflected downwardly as beam 86, it is applied to electrooptical digitaldeflector 98 where it can be deflected as beam 94 or beam 96. Thedirection in which the beams are deflected by deflectors 82, 88 and 98will depend upon the states of electrical signals applied thereto vialeads 97; and these signals, in turn, are controlled by a synchronizer99 mechanically coupled to the rotating shaft 72. Let us assume, forexample, that there are eight lenses spaced around the periphery of disc70. During the first full revolution of disc 70, the electrical signalsapplied to deflectors 82 and 88 will be such as to cause deflector 82 todeflect the beam upwardly as beam 84 and cause deflector 88 to deflectits incident beam upwardly as beam 90. Now, as the disc rotates, passageof each lens 80 past the incident beam will cause a scan 101 to beproduced in Group I of the field of view, the respective scans 101 beingone below the other because of the variable off-axis positioning of thelenses (i.e., the angles B) about disc 70.

Following the first complete revolution of disc 70, synchronizer 99alters the signals to the deflectors such that beams 84 and 92 aregenerated, thereby producing the scan lines in Group II of the field ofview during the second revolution of the disc 70. On the thirdrevolution, beams 86 and 94 are produced to generate the scan lines inGroup III of the field of view and during the fourth revolution beams 86and 96 are produced to generate the scan lines in Group IV. At thispoint, the cycle repeats through four revolutions of disc 70, startingat the top of Group I.

The number of horizontal scan lines that can thus be generated is equalto 2 times the number of lenses 80, N being the number of binarydeflecting stages in cascade that are employed. In the example given inFIG. 5, for example, N is 2; and assuming that the number of lenses 80is eight, then 32 horizontal scan lines can be produced in the scanpattern in succession.

FIG. 6 depicts another scanner version that may be used to achieve thesame pattern. Here, again, a plurality of lenses is circumferentiallyspaced around the periphery of a rotating disc 102, each lens being atan angle B with respect to horizontal, and the respective angles [3varying for each lens 100 spaced around the disc 102. In this case, astationary light beam 104 passes through a stationary lens 106 andthence to an electrically controlled analog deflector 108. From thedeflector 108 the beam is focused into a spot on the reflecting facetsof a truncated pyramid I10 and thence through the lenses 100. With thearrangement shown, the optical assembly will generate a scan patternsuch as that shown in Group I of FIG. 5 as the disc 102 rotates throughone complete revolution. After the first revolution is completed, theanalog deflector 108, through synchronizer 109, causes the beam to bedeflected in a discrete step along the radius of the disc 102, whereupona second group of scan lines is generated below. or above, the first. Inthis manner, the angle generated in the ver tical direction is limitedonly by the extent to which the analog device may deflect the beamacross the focal plane of the optical element without incurring severeoptical distortion. Here, again, the output optical elements on theperiphery of disc 102 may be either spherical mirrors or lenses. Thelenses may either collimate the beam or, following collimation, focusthe beam at a distant point.

As will be understood, in the embodiments of the invention described tothis point, the field of view of the scanner can be changed only indiscrete increments and then at a considerable cost in mechanicalcomplexity. Each incremental change will require directing the incidentbeam to a separate rotating element that has a different number offacets and, upon reflection, redirecting the beam back to the axis ithad originally traversed. The lens cannot be used to modify the angulardeflection of the collimated beam since the beams diameter at its pointof origin is the same as its transmitted diameter. A

lens placed in the path of the beam and focused at the beams I origindoes not see a point source and, therefore, degrades the beam scollimation.

The angle generated by rotational-refractive scanners actuallyoriginates at a point source. A lens placed between this point and theoutput optical element can change the focal length of the output elementwithout comprising the ability of the element to collimate the beam. Thelens, in conjunction with appropriate refractive devices placed aboutboth the output element and the stationary input lens may bevaried suchthat the field of view is continuously changed while the collimation ofthe beam is retained.

FIG. 7 shows an optical schematic of a rotationalrefractivetype scannerand depicts the manner in which the optical relationships can be changedto alter the scanners field of view. One field of view in FIG. 7 isidentified by the angle and the smaller. reduced field of view isindicated by the angle 0. The output optical element, comprising a lens110 mounted on the periphery of a rotating disc 112 as shown in FIG. 8has a diameter D; while an input stationary lens 114 has a diameter d.As the focal length of the output element increases. the field of viewdecreases. Thus, as the focal length of lens 110 changes from F to F,the field of view decreases from the angle 6 to the angle 0. At the sametime, the f-number of the beam must remain constant in the process. Thatis:

fis the focal length oflens 114 for the angle 0 and j is the focallength of the lens 114 for the angle 0.

FIG. 8 illustrates the manner in which the optical elements are coupledin a practical application. The system again includes a truncatedpyramid 116, and a rotating polygon 118 for scanning in the verticaldirection. On either side of the input lens 114 are translatingrefractive elements 120 and 122; and on opposite sides of the outputlens 110 is a second pair of translating elements 124 and 126. Theelements 120, I22, 124 and 126 are mechanically coupled to a drive motor128 along with the input lens 114. The input lens 114 is moved furtherout in the beams path and then varies in concert with the positions ofthe refractive elements 120-126. The focal length of the output lens 110may, therefor, be continuously increased or decreased in this fashionand its field of view continually changed as a consequence. Thecollimation of the beam is preserved since both the input lens and theoutput lens always share the same focal plane.

Although the invention has been shown in connection with certainspecific embodiments, it will be readily apparent to those skilled inthe art that various changes in form and arrangement of parts may bemade to suit requirements without departing from the spirit and scope ofthe invention.

I claim as my invention:

1. In a two-dimensional optical scanning'system, a rotating disc, aplurality of lenses carried on said disc and spaced around its peripheryin side-by-side relationship, pyramid means at the center of said discand operatively connected thereto so as to rotate therewith, the sidesof said pyramid means defining a number of plane reflecting facets equalto the number of lenses. each facet being located at the focal plane ofan associated lens, and means for producing a light beam and forfocusing said beam into a spot which intersects the focal planes of saidlenses on said reflecting facets such that the beam of light will bereflected in one dimension from each facet to its associated lens sothat the principal axis of said lens is initially on one side of thebeam, then coincident with it, and finally on the other side of thebeam, whereby the angle scanned by the beam in said one dimension willcomprise the angle through which the beam is deflected as the lensrotates through the angle it subtends plus the refractive anglesproduced by virtue of the initial and final off-axis positions of thebeam with respect to the principal axis of the lens, and means in thepath of said beam for causing said beam to scan in a second dimension atright angles to said first dimension.

2. The system of claim 1 wherein the means for causing said beam to scanin said second direction comprises a rotating polygon having a pluralityof reflective facets interposed between said means for producing a lightbeam and the rotational path of travel of said facets.

3. The system of claim 2 wherein said polygon rotates at a higher speedthan said rotating disc.

4. The system of claim 1 wherein said means for causing the beam to scanin a dimension at right angles to the first-mentioned dimensioncomprises a plurality of electrooptical beam deflectors arranged incascade.

5. The system of claim 4 wherein the beam at the output of said lensesis directed to a first beam deflector capable of deflecting the beam toeither a second or a third beam deflector, the second and third beamdeflectors each being capable of deflecting the beam to either a firstor a second position.

6. The system of claim 4 wherein each lens is disposed at an angle withrespect to a line normal to the plane of rotation of said rotating disc,said angles being difi'erent for each lens.

7. The system of claim 1 wherein each of said lenses is disposed at anangle with respect to a line extending normal to the plane of rotationof said rotating disc with each of said angles for the respective lensesbeing different from the angles for the other lenses.

8. The system of claim 7 including an analog electrooptical deflectorfor deflecting an incident beam from one position to another on thefacets of said rotating truncated pyramid each time said rotating discrotates through a complete revolution.

9. The system of claim 1 including means for continually increasing ordecreasing the field of vieyv of said lenses.

10. The system of claim 9 wherein the means for directing said lightbeam into the rotational path of travel of said facets includes an inputlens. translating refractive elements on either side of said input lens,translating refractive elements on either side of the rotational path oftravel of said lenses carried on the disc and in the path of said lightbeam, and means for moving said input lens and said translatingrefractive elements in unison.

1. In a two-dimensional optical scanning system, a rotating disc, aplurality of lenses carried on said disc and spaced around its peripheryin side-by-side relationship, pyramid means at the center of said discand operatively connected thereto so as to rotate therewith, the sidesof said pyramid means defining a number of plane reflecting facets equalto the number of lenses, each facet being located at the focal plane ofan associated lens, and means for producing a light beam and forfocusing said beam into a spot which intersects the focal planes of saidlenses on said reflecting facets such that the beam of light will bereflected in one dimension from each facet to its associated lens sothat the principal axis of said lens is initially on one side of thebeam, then coincident with it, and finally on the other side of thebeam, whereby the angle scanned by the beam in said one dimension willcomprise the angle through which the beam is deflected as the lensrotates through the angle it subtends plus the refractive anglesproduced by virtue of the initial and final off-axis positions of thebeam with respect to the principal axis of the lens, and means in thepath of said beam for causing said beam to scan in a second dimension atright angles to said first dimension.
 2. The system of claim 1 whereinthe means for causing said beam to scan in said second directioncomprises a rotating polygon having a plurality of reflective facetsinterposed between said means for producing a light beam and therotational path of travel of said facets.
 3. The system of claim 2wherein said polygon rotates at a higher speed than said rotating disc.4. The system of claim 1 wherein said means for causing the beam to scanin a dimension at right angles to the first-mentioned dimensioncomprises a plurality of electrooptical beam deflectors arranged incascade.
 5. The system of claim 4 wherein the beam at the output of saidlenses is directed to a first beam deflector capable of deflecting thebeam to either a second or a third beam deflector, the second and thirdbeam deflectors each being capable of deflecting the beam to either afirst or a second position.
 6. The system of claim 4 wherein each lensis disposed at an angle with respect to a line normal to the plane ofrotation of said rotating disc, said angles being different for eachlens.
 7. The system of claim 1 wherein each of said lenses is disposedat an angle with respect to a line extending normal to the plane ofrotation of said rotating disc with each of said angles for therespective lenses being different from the angles for the other lenses.8. The system of claim 7 including an analog electrooptical deflectorfor deflecting an incident beam from one position to another on thefacets of said rotating truncated pyramid each time said rotating discrotates through a complete revolution.
 9. The system of claim 1including means for continually increasing or decreasing the field ofview of said lenses.
 10. The system of claim 9 wherein the means fordirecting said light beam into the rotational path of travel of saidfacets includes an input lens, translating refractive elements on eitherside of said input lens, translating refractive elements on either sideof the rotational path of travel of said lenses carried on the disc andin the path of said light beam, and means for moving said input lens andsaid translating refractive elements in unison.